Method and Apparatus for Processing Fluid from a Well

ABSTRACT

An assembly is for an oil and gas production platform or rig and related methods. The platform or rig may have a Christmas tree deck and a hatch deck above the Christmas tree deck. The assembly may have a Christmas tree connected to a top of a wellhead on the platform or rig located at the Christmas tree deck. The assembly may further have a processing unit comprising at least one separator, positioned above and connected onto a top of the Christmas tree. The Christmas tree may bear at least partially the weight of said separator. The separator may be operable for receiving production fluid from at least one oil and gas production well and removing solids to clean the production fluid.

TECHNICAL FIELD

The present invention relates generally to the processing of fluid fromwells. In particular, it relates to the processing, removal, anddisposal of solids such as sand and sediments from fluid such asproduction fluid extracted from a well, and to apparatus and methods toperform such processing on rigs, platforms, and/or onshore or subseastructures.

BACKGROUND

In the oil and gas exploration and production industry, fluid travelsout of and is extracted from a wellbore in various situations. Duringhydrocarbon production for example, production fluid containinghydrocarbons from a subterranean reservoir are conventionally producedby a well, driven to the surface along the well by the pressure from thesubsurface. The fluid exits the well from a wellhead, passes through avalve tree (typically termed the ‘Christmas’ tree), and is directedthrough transport pipes to a processing system for processing the fluidto bring the hydrocarbons into condition for export to end users. Inoffshore environments, depending on the type of well, the wellhead maybe positioned subsea at the seabed, or on the well floor of a productionplatform.

Typically, the wellhead has the valve tree mounted upon it, providing anaccess point to the well and containing valves for closing and sealingthe well with double-pressure barriers. Normally, the valve tree has theability to allow connection of service or intervention equipment via the“service wing” inlet of the valve tree while production can continuewith a flow of produced fluid from the reservoir via the “productionwing” outlet of the valve tree. When servicing is required, access viathe service wing is provided through the opening of the appropriatevalves.

The produced fluid from the well passes from the valve tree through aproduction choke, typically a series of production chokes, which is usedto control the flow of fluid from the well and is arranged to be closedto stop the flow of production fluid from the well if required. It mayalso be used to reduce or increase the rate of flow of production fluid.

A particular challenge during production is that the composition of theproduction fluid is generally a mixture of liquid and gas, often withsome solids such as sand particles entrained in the fluid. Theprocessing system downstream from the valve tree is provided to processthe fluid and may include various stages of separation etc., to removeunwanted solids, and separate gas from liquid hydrocarbon components. Adifficulty is that the composition of the fluid from the well can changeover time and may not be predictable. Therefore, the processing systemmay typically be poorly suited for handling such changes or certaintypes of flow. Moreover, multiple wells may be connected to oneprocessing to system, and the composition of fluid between differentwells may be widely different, as can quantities of solids.Collectively, such changes can result in the processing system beingincapable of managing the production process as originally intended.Accordingly, there is a need for alternative methods to be explored toaccommodate the production changes.

In addition, as a reservoir depletes over time, the amount of solids inthe production fluid can tend to increase. These solids typicallycomprise grains of rock or minerals, e.g. sand, from the geologicalformation of the subsurface that the wellbore penetrates. For instance,the grains of rock or minerals, e.g. sand, may come from the reservoirformation and enter the wellbore together with hydrocarbon fluid fromthe formation. The presence of such solids in the production fluid cangive rise to problems in handling by the processing system and can causeabrasion and damage to pipework and related components. To address this,a typical approach is to reduce the rate of flow from the well, whichreduces the tendency to draw solids out of the well with the productionallowing the processing system to process the fluid. But, lower rates ofhydrocarbon production are achieved as a result.

On some platforms, additional separation equipment is installed whenrequired to handle the increased production of solids. For examplededicated solids separation units such as a de-sander used on atemporary basis, in order to remove solids and in particular producedgrains of formation rock or sand from the flow of production fluidbefore the production fluid enters the normal processing system furtherdownstream. Use of equipment such as de-sanders or similar devices cantherefore allow for higher production rates.

Deck space on offshore platforms is often limited and at a premium. Inmany cases, any need for de-sanders or similar devices to promoteproduction may not have been foreseen in early platform designs. Assuch, de-sanders on early platforms have simply been placed in deckareas wherever available, with temporary pipework being installed andconfigured to divert production fluid out of the permanent productionsystem into the de-sander and then back into the permanent productionsystem once the solids are removed by the de-sander.

However, the provision of de-sanders in this manner may not beconvenient or efficient. Typically, the flow of fluid passes throughsignificant lengths of pipework and through valves such as theproduction choke, and with formation rock fragments present exposes suchcomponents to abrasion and damage. Therefore, even with a de-sanderinstalled as described above, production rates may need to be lowered topreserve related components and equipment.

An example de-sander is described in patent publication numberWO03099448 (Arefjord).

SUMMARY OF THE INVENTION

In light of the above, according to a first aspect of the inventionthere is provided apparatus comprising: at least one separator forreceiving fluid from at least one well and removing solids to clean thefluid. The apparatus may further comprise at least one body to which theseparator is connected, for supporting and arranging the separator inposition with respect to a valve tree which is connected to a wellhead.The separator may typically be arranged to be at least partiallysupported in use by the valve tree. The apparatus may be furtherconfigured so that when installed the apparatus and the valve tree arepositioned on a common, vertical axis.

According to a second aspect of the invention there is providedapparatus configured to be installed on a structure in which an accesshatch is provided for accessing a valve tree which is connected to awellhead. The access hatch may have a vertical axis extendingtherethrough. The apparatus may comprise at least one separator forreceiving fluid from at least one well and for removing solids to cleanthe fluid. The apparatus may be further configured so as to bepositioned on the vertical axis.

The apparatus may be configured to fit through an opening of the accesshatch. The separator, or at least one tank of the separator, may beconfigured to fit through an opening of the access hatch.

The apparatus or part thereof may be arranged to be positioned above theaccess hatch when installed. The separator or part thereof may bearranged to be positioned below the access hatch when installed. Theseparator may be arranged to be positioned within the lateral extent ofthe access hatch when installed.

The apparatus may further comprise a hub or processing unit forprocessing fluid in which the separator may be mounted together withanother component selected from any one or more of: a choke; anemergency shut down valve; and a flow line, a valve, or other equipmentfor operating the separator.

The body may comprise a mount for the separator and optionally anothercomponent, e.g. one of the other components of the hub. The body may bearranged to connect to the valve tree, or to a riser extending from thevalve tree, for providing either or both of fluid and physicalconnection with the valve tree. The body may be arranged to connect to atop of the valve tree, or connect to an upper end of a vertical bore ofthe valve tree.

The body may comprise at least one connector for connecting with thevalve tree. The connector may be arranged to connect to a top of thevalve tree, or connect to an upper end of a vertical bore of the valvetree. The body may have a bore for conveying fluid from the well betweenthe valve tree and the separator, e.g. from the valve tree to theseparator. The body may comprise a pipe section. The bore may be a boreof the pipe section.

The body may be configured to attach to the valve tree so that the boremay be aligned or concentric with a vertical bore of the valve tree toallow for full diameter access to the vertical bore, e.g. for loweringequipment (e.g. a work string) through the aligned or concentric boresand into the wellbore.

The separator may be mounted so as to be offset laterally with respectto a vertical bore of the valve tree for allowing full diameter accessthrough the vertical bore of the valve tree if required when theapparatus is installed. The full diameter access may be provided asdescribed anywhere else herein.

The separator may be mounted to be offset laterally from the bore in thebody of the apparatus so as to allow the full diameter access to beobtained via the bore in the body of the apparatus.

The at least one separator may comprise first and second separators eachcomprising respective first and second tanks for cleaning the fluid fromthe well. The separator may comprise a de-sander.

The fluid from the well may be any of: production fluid; drilling fluid;well stimulation fluid; and circulation fluid.

The access hatch may be provided on a deck of the structure. Thestructure may be one of a subsea template; an offshore platform or rigabove the sea surface; and an onshore platform. The platform or rig maybe an oil and gas platform or rig, e.g. an oil and gas productionplatform or rig.

According to a third aspect of the invention there is provided anassembly comprising: a valve tree connected to a wellhead of a well; andapparatus. The apparatus may be as set out in any other aspect of theinvention. The apparatus may be for processing fluid from at least onewell. The apparatus may be a processing unit or hub as defined inrelation to any aspect of the invention herein. The apparatus maycomprise at least one separator for receiving said fluid from the well,and the separator may be operable for removing solids to clean thefluid.

The separator may preferably be arranged to be at least partiallysupported in use on a valve tree which is connected to a wellhead. Morespecifically, the processing unit or hub and/or the separator may be atleast partially supported, optionally via a riser, on an upper end of avertical bore of the valve tree. In this way, the valve tree may bear atleast some part of the weight of the apparatus and/or the separator,when the apparatus is installed. In one embodiment, the assembly may bean assembly for an oil and gas production platform or rig. The platformor rig may have a Christmas tree deck and a hatch deck above theChristmas tree deck. In such an embodiment, the assembly may comprise aChristmas tree connected to a top of a wellhead on the platform or rig;and a processing unit or hub which may comprise at least one separator.The Christmas tree may be located at the Christmas tree deck. Theseparator may be positioned above and be connected to a top, or to anupper end of a vertical bore, of the Christmas tree. The Christmas treemay bear at least partially the weight of said separator. The separatormay be operable for receiving production fluid from at least one oil andgas production well and removing solids to clean the production fluid.

In another embodiment, the assembly may comprise: a Christmas treeconnected to a top of a wellhead; and a processing unit comprising atleast one separator. The Christmas tree may have a vertical bore foraccessing the well by an intervention or another tool. The tool may belowered on a wireline or tubing into and/or through said tree from alocation where the tool is located above the vertical bore of theChristmas tree. The separator may be positioned above and be connectedto a top, or to an upper end of a vertical bore, of the Christmas tree.The Christmas tree may bear at least partially the weight of saidseparator. The processing unit may be further arranged to provide fulldiameter access to the vertical bore of the Christmas tree. Theseparator may be operable for receiving oil and gas production fluidfrom at least one well and removing solids to clean the productionfluid. Also in this embodiment, the assembly may be an assembly on anoil and gas production platform or rig. The platform or rig may have aChristmas tree deck and a hatch deck above the Christmas tree deck. TheChristmas tree may be arranged at the Christmas tree deck.

The separator may comprise a de-sander. The de-sander may be a cyclonicde-sander. More specifically, the de-sander may be arranged to produce acyclonic or rotational flow of the fluid about a vertical axis. Thede-sander may comprise a tank, e.g. a processing tank. The cyclonic orrotational flow may be produced on a vertical wall of the tank of thede-sander. The flow may be obtained inside the tank of the de-sander.The flow may be produced in a region between a screen and the wall ofthe tank. The screen may typically be a cylindrical screen arrangedvertically in the tank. During operation of the de-sander, the solidsmay drop out of the cyclonic or rotational flow, e.g. under the force ofgravity. The fluid may be production fluid which may includehydrocarbons from a subterranean hydrocarbon reservoir. The solids maycomprise formation rock particles or fragments, e.g. sand, from asubterranean formation.

The tank may be a cylinder which may be vertical. Accordingly, oppositeends of the cylinder may be arranged vertically one above the other. Acylindrical body of the cylinder may extend longitudinally between theends. The interior of the cylindrical body of the tank may comprise acylindrical space. In use, the flow may be produced on a vertical wallof the interior of the cylindrical body of the tank.

The solids may fall to a base of the tank. The processing unit mayinclude a collector for collecting the solids which drop out of thecyclonic or rotational flow. The collector may comprise a tank, e.g. aprocessing tank, arranged below the tank of the de-sander. The solidsmay be transferred under gravity from the tank of the de-sander to thetank of the collector.

The de-sander may be a dynamic de-sander. The de-sander may have arotatable body in the tank of the de-sander. The rotatable body mayimpart a component of force on the fluid received when rotated. Theimparted component of force may facilitate to drive the fluid toward avertical wall of the tank, e.g. urging the fluid in the flow radiallyoutwardly toward the wall. The rotatable body may comprise at least oneimpeller, blade, or fin. The rotatable body may preferably be rotatableabout a vertical axis. The impeller, blade, or fin may facilitateimparting the component of force for driving the fluid laterally outwardtoward the wall. The rotatable body may be driven to rotate by a motor.The rotatable body may be disposed on a shaft which may be coupled tothe motor. The motor may operate to rotate the shaft about itslongitudinal axis, for rotating the body. The shaft may be arranged withthe longitudinal axis arranged vertically. The rotatable body may befitted on an inside of the screen in the tank. The screen may have oneor more openings through a wall, typically a vertical wall, of thescreen. The rotatable body may drive the fluid through the opening(s) inthe wall of the screen. The screen may be fixed with respect to thetank, and the rotatable body may thus rotate relative to the screen (andthe tank).

The de-sander may have the tank mounted in the processing unit. Thede-sander may have an associated collector or solids container, whichmay comprise a tank for containing removed solids transferred from thede-sander in order to be later disposed of.

The de-sander may be a first de-sander and the processing unit mayfurther comprise a second de-sander. The second de-sander may havefurther features as defined above in relation to the first de-sander.For example, either or both of the first and second de-sanders mayproduce a cyclonic flow and may be a dynamic de-sander. The first andsecond de-sanders may be operable in parallel to clean the productionfluid.

The processing unit may include a degasser comprising a processing tank,for removing gas from the production fluid upstream from a de-sander.

The processing unit may have a vertical conduit or passageway alignedwith the vertical bore of valve tree. The vertical bore may be fordeploying an intervention or other tool on a wireline or tubing into thevalve tree.

The processing unit may comprise a vertical conduit. The verticalconduit may be aligned with a vertical bore of the valve tree. The tankof the de-sander and the tank of the solids container or collector maybe spaced apart in the processing unit along the conduit or passageway.The tank of the separator (e.g. de-sander) may extend longitudinallyalong the vertical conduit or passageway. The conduit or passageway maycomprise a vertical pipe section.

In embodiments providing full bore access or full diameter access, theconduit or passageway may be arranged so that the intervention tool orother tool may be lowered from the conduit or passageway into the valvetree, such that an intervention or other tool may be inserted and mayutilise or occupy the full inner diameter of the vertical bore of thevalve tree. The internal diameter of the passageway or conduit may thusbe equal to or exceed the internal diameter of the vertical bore of thevalve tree. The intervention or other tool may then be arranged to bedelivered into the wellhead in an arrangement where the main bore of thevalve tree is accessible in its full diameter over its full length. Thepassageway or conduit and/or bore of the valve tree may then not provideany restriction to passage of the tool therethrough. Such a restrictionmay be considered a localised narrowing then widening of the diameter ofthe bore of the valve tree and/or passageway or conduit (in thedirection toward the wellhead), or may be an obstacle in the middle ofthe bore. Such restriction may be created in particular modes ofoperation, e.g. by a flow tube which may be inserted fully or partiallyinto the bore of the valve tree. The inserted flow tube may thus preventfull diameter access to the wellhead at certain times of use, but may beremoved at other times to provide full diameter access.

The processing unit may comprise a connector. The connector may be forconnecting the processing unit onto the top of the valve tree, or to anupper end of a vertical bore of the valve tree. The connector may thusconnect the processing unit to the valve tree at the top of the valvetree or the upper end of the vertical bore of the valve tree. Theconnector may be configured to mate with a top flange of an upper boreportion of the vertical bore of the valve tree. The processing unit maycomprise a mount for mounting the separator therein. The processing unitmay further comprise either or both of an emergency shut down valve anda choke.

According to a fourth aspect of the invention there is provided a methodof equipping a valve tree for processing fluid from at least one wellusing the apparatus as set out in any other aspect of the invention, orthe assembly as set out in any other aspect of the invention.

In embodiments in which the assembly may include a processing unit, themethod may comprise applying the processing unit to the valve tree suchthat the separator can be at least partially supported on the valvetree, whereby said valve tree may bear at least part of the weight ofthe separator. More specifically, the processing unit and/or theseparator may be at least partially supported on an upper end of avertical bore of the valve tree.

The method may be performed to equip the valve tree on an oil and gasproduction platform or rig, wherein the platform or rig may have a valvetree deck and a hatch deck above the valve tree deck, and the valve treemay be arranged at the valve tree deck. The method may then include thestep of lowering the processing unit through a hatch in the hatch deckonto the valve tree, so as to locate the separator in place, at leastpartially supported on the top of or on the upper end of a vertical boreof the valve tree.

The method may comprise the steps of:

-   -   providing the apparatus as set out in any other aspect of the        invention;    -   positioning the apparatus with respect to the valve tree, to        position the apparatus in an operating position in which the        separator is operable to receive and clean the fluid.

The method may further comprise letting the valve tree at leastpartially support the separator, in said operating position.

According to a fifth aspect of the invention there is provided a methodof providing an assembly for processing fluid from at least one well,the assembly comprising the apparatus as set out in any other aspect ofthe invention and a valve tree. The assembly may be to be provided on astructure in which an access hatch may be provided for accessing thevalve tree. The access hatch may have a vertical axis extendingtherethrough. The method may comprise the steps of: providing theapparatus as set out in any other aspect of the invention; andpositioning the apparatus in an operating location in which theseparator may be operable to receive and clean the fluid, whereby in theoperating location, the positioned apparatus may be positioned on thevertical axis.

The method may further comprise lowering the apparatus and/or theseparator through an opening of the access hatch to position theapparatus in the operating location. The apparatus may be connected inplace so that the apparatus and/or the separator may be arranged withina lateral extent of the access hatch. The method may further compriseconnecting the apparatus to the valve tree so as to be supportedthereupon.

According to a sixth aspect of the invention there is provided a methodof performing an operation, e.g. performing an intervention operationthrough the vertical bore of a valve tree of any of the aspects. Theoperation may be performed in a well while the apparatus as set out inany other aspect or as applied in any other aspect remains in place.

The intervention operation may be performed by lowering interventionequipment through the vertical bore of the valve tree. The operation maybe performed with the separator in place and being at least partiallysupported on the top of the Christmas tree.

The operation may comprise either a well intervention operation or adrilling operation, and may include accessing the well with equipmentfor intervention or drilling via an access bore in communication withthe wellhead, the separator being laterally offset with respect to theaccess bore.

According to a seventh aspect of the invention, there is provided anassembly comprising a valve tree which is connected to a wellhead andapparatus comprising at least one separator for receiving fluid from atleast one well and removing solids to clean the fluid, wherein theapparatus and the valve tree are positioned on a common, vertical axis.

According to an eighth aspect of the invention there is provided anassembly comprising:

-   -   at least one valve tree; and    -   apparatus comprising at least one separator for receiving fluid        from at least one well and removing solids to clean the fluid.        At least part of the apparatus may be located in a region        between a valve tree deck on which the valve tree may be        provided, and a hatch deck, which may be adjacent to and overlie        the valve tree deck. The hatch deck may be configured for        accessing the valve tree through at least one hatch.

According to a ninth aspect of the invention, there is provided a methodof processing fluid from at least one well, the method comprising thesteps of:

-   -   providing at least one separator which is arranged to receive        the fluid from the well downstream from at least one wellhead;        and    -   using the separator to remove solids from the fluid, to produce        a cleaned fluid which travels downstream on a flow path from the        separator through either or both of: a valve tree on the        wellhead from which the separator receives the fluid; and a        valve tree on another wellhead.

In a preferred embodiment, the well may have a wellhead, and a Christmastree may be disposed on the wellhead, and the method may comprise thesteps of:

-   -   providing at least one separator, receiving the production fluid        in the separator downstream from the wellhead and the Christmas        tree, the production fluid travelling through a Christmas tree        on said wellhead to the separator; and    -   using the separator to remove solids from the production fluid,        to produce a cleaned production fluid which may travel        downstream on a flow path from the separator through either or        both of: the Christmas tree on said wellhead from which the        separator receives the production fluid; and a production        Christmas tree on another wellhead.

The method may further include using the separator to remove gas fromthe fluid in order to produce the cleaned fluid. The method may furthercomprise cleaning the removed solids to remove contaminants so as toallow disposal. The cleaned fluid from the separator may travel througha well choke operable to control extraction of the fluid from the well.The flow path may be provided via a tube inserted into the valve tree,e.g. the Christmas tree. At least one tank of the separator may bemounted above the valve tree so as to be supported thereupon.

According to a tenth aspect of the invention there is provided apparatusfor processing fluid from at least one well, the apparatus comprising:

-   -   at least one separator for receiving the fluid from the well        downstream from at least one wellhead, the separator being        operable for removing solids from the fluid for producing a        cleaned fluid; and    -   a flow path for the cleaned fluid to travel downstream from the        separator through either or both of: a valve tree on the        wellhead from which the separator receives the fluid; and a        valve tree on another wellhead.

In a preferred embodiment, the well may have a wellhead and a Christmastree may be disposed on the wellhead, and the apparatus may comprise:

-   -   at least one separator for receiving the production fluid from        the well downstream from the wellhead and the Christmas tree,        wherein the production fluid, in use, may travel to the        separator through a Christmas tree on the wellhead, the        separator being operable for removing solids from said fluid for        producing a cleaned production fluid; and    -   a flow path for the cleaned production fluid to travel        downstream from the separator through either or both of: the        Christmas tree on said wellhead from which the separator        receives the production fluid; and a production Christmas tree        on another wellhead.

The flow path may be obtained by a tube inserted into the valve tree.

The valve tree may have a bore through which fluid can travel from thewellhead to the separator. The bore may be a vertical bore. The tube maycomprise a bridge tube arranged to bridge radially across the bore ofthe valve tree. The cleaned fluid from the separator may pass throughthe bridge tube to exit the valve tree.

The valve tree may have a service wing and a production wing. The bridgetube may be inserted to span between respective bores of the service andproduction wings for allowing the cleaned fluid from the separator topass through the bridge tube and exit the valve tree from the productionwing.

The bridge tube may be removed from operation if required, e.g. forallowing full diameter access to the well through an access bore of thevalve tree.

The apparatus may further comprise an actuator configured to be mountedto the valve tree for inserting the bridge tube into the access bore foroperation, or retracting the bridge tube from operation so as not toobstruct the access bore. The access bore may be a vertical bore of thetree.

The valve tree may have a vertical access bore for accessing the wellfrom above. The tube may be inserted into the access bore of the treealong the access bore. The production fluid to be cleaned may travelthrough the tube to the separator. The apparatus may further comprise astinger which may include the tube. The stinger may be arranged todeliver the tube into position so as to insert the tube into thevertical access bore of the tree. Said tube may be an inner tube of thestinger and may be removable from an outer tube of the stinger. This mayfacilitate removal of the inner tube from the valve tree, and/or mayfacilitate allowing full diameter access to the access bore of the valvetree through the outer tube. The inner tube may be arranged to be fishedout of the stinger by deploying fishing equipment.

The apparatus may further comprise a body having a bore. The body may bearranged to mate with the valve tree so that the bore may be alignedwith a bore of the valve tree for fluid from the well to travel to theseparator through the bore. The body may comprise a pipe section. Thebore may be a bore of the pipe section.

The separator may be mounted to the body. The body may comprise a riser,or may be arranged to connect with a riser, the riser being connected tothe valve tree so that fluid from the well can travel through a sectionof the riser, to the separator to clean the fluid. The riser may be anintervention riser, and the apparatus may be configured to allow accessto the well through the riser to perform an intervention, in anintervention mode, if desired.

The apparatus may further comprise a tube of a stinger arranged along abore of the valve tree or a tube for bridging across a bore of the valvetree, wherein the tube may be removable out of operation, to allow anintervention to be performed with full diameter access through the borein the intervention mode.

The apparatus may further comprise either or both of an emergency shutdown valve and a well choke along the flow path downstream from theseparator.

The apparatus may further comprise a hub or processing unit, in whichmay be mounted any one or more of:

-   -   the separator and/or at least one tank thereof; an emergency        shut down valve; a well choke; and at least one connecting body,        e.g. a connector. The connecting body or connector may be for        mating with the valve tree, e.g. for either or both conveying        fluid from the well to the separator and supporting at least        partially the weight of the hub or processing unit or separator        upon the valve tree. The hub or processing unit may be as        described anywhere else herein.

The processing unit or hub and/or the separator may be supported on thevalve tree as described anywhere else herein. For instance, theprocessing unit or hub and/or the separator may be at least partiallysupported, optionally via a riser, on an upper end of a vertical bore ofthe valve tree. The separator may comprise a cyclonic or dynamicseparator.

The separator may comprise a de-sander. The de-sander may be asdescribed anywhere else herein, e.g. it may be a cyclonic de-sander.

The fluid may be any of: production fluid; drilling fluid; wellstimulating fluid; and circulation fluid. The production fluid maycomprise hydrocarbons recovered from the subsurface of the earth, e.g.from a subsurface oil and gas reservoir. The production fluid maycomprise oil and/or gas from the reservoir. The production fluid mayinclude the solids entrained and carried in the fluid in a flow from thewellbore toward the surface. At the surface, the production fluid maypass through the production wellhead, and then through the valve treeconnected to the top of the production wellhead.

The solids may be as described anywhere else herein. For example, thesolids may comprise particles, fragments, or grains of rock or mineralse.g. sand from the subsurface formation penetrated by the wellbore. Theparticles, fragments, or grains of rock may be carried with a flow ofhydrocarbon fluid.

The de-sander may operate to separate solids other than sand. Typically,the solids which may be separated from the production fluid by thede-sander may include sand or may include particles which have the sameor similar characteristic to that of sand, such as the same or similarclass of grain size, density, or mineralogical composition. In otherwords, the de-sander may cause other particles which are of same orsimilar character as sand to separate out.

According to an eleventh aspect of the invention there is provided amethod of processing fluid from at least one well, the method comprisingthe steps of:

-   -   (a) providing at least one separator arranged to receive fluid        from the well; and    -   (b) removing solids from the fluid using the separator, to        produce cleaned fluid upstream of a choke for the well from        which fluid is received or for another well.

According to a twelfth aspect of the invention there is providedapparatus for processing fluid from at least one well, the apparatuscomprising:

-   -   at least one separator for receiving said fluid from the well,        the separator being operable for removing solids from the fluid        for producing cleaned fluid; and    -   a flow path for the cleaned fluid to travel downstream via a        choke for the well from which fluid is received or for another        well.

The fluid from the well may therefore not pass through the choke beforethe fluid has been cleaned by use of the separator. The choke maypreferably operate on the cleaned fluid. The choke may operate tocontrol the flow and/or pressure in the wellbore. The choke maytypically not operate on the fluid from the well before it has beencleaned by the separator.

According to a thirteenth aspect of the invention, there is providedapparatus comprising at least one separator arranged to be at leastpartially supported in use by a valve tree which is connected to awellhead, the separator being operable for receiving fluid from at leastone well and removing solids to clean the fluid. In this way, the valvetree may bear at least some part of the weight of the apparatus and/orthe separator, when the apparatus is installed.

According to a fourteenth aspect of the invention, there is provided amethod of using the apparatus as set out in relation to any aspectherein, the method comprising the steps of:

-   -   providing the flow path; and    -   processing fluid using the apparatus by:        -   receiving the fluid in the separator;        -   operating the separator to remove solids from the fluid to            produce cleaned fluid; and        -   letting the cleaned fluid from the separator travel            downstream via the provided flow path.

Preferably, the apparatus may be used to process fluid from the wellwhich may have a wellhead and a valve tree, e.g. a Christmas tree,disposed on the wellhead. The fluid may be received in the separatordownstream from the wellhead and the valve tree. The production fluidmay travel through the valve tree on the wellhead to the separator. Thevalve tree may comprise a Christmas tree, e.g. as described anywhereherein. The fluid may comprise production fluid. The cleaned fluid maytravel downstream on the flow path through the valve tree on thewellhead from which the separator receives the fluid and/or a productionChristmas tree of another wellhead.

The flow path may be provided by inserting a tube into the valve tree.The tube may be a flow tube. The tube may be inserted by inserting astinger into a vertical bore of the valve tree. The tube may be insertedby inserting a bridge tube across a bore of the valve tree.

The fluid may be received in the separator by opening a valve to directthe fluid from the valve tree to the separator. The fluid may traveldownstream by opening an exit line from the separator.

The method may further comprise:

-   -   halting the processing of the fluid;    -   removing the flow path to allow full bore access through a        vertical bore of the valve tree; and    -   performing an intervention or drilling operation in the well by        delivering equipment through the vertical bore and into the well        while the separator remains in place.

The flow path may be removed by removing or moving an inserted tube fromthe vertical bore of the valve tree, and wherein the equipment may bedelivered into the well via the vertical bore.

The method may further comprise, after the intervention or drillingoperation has been performed and the equipment has been removed,re-establishing the flow path for cleaned fluid to travel downstreamfrom the separator; and re-commencing the processing of fluid from thewell using the separator.

The valve tree may be as described anywhere else herein. The well chokemay be as described anywhere else herein. The separator may comprise adevice as described in the claims of WO03099448 (Arefjord), or may beoperated to perform a method as described in the claims of WO03099448(Arefjord).

In another aspect, there is provided a hub or a processing unit forprocessing fluid from at least one well, the hub or processing unitbeing configured to be connected to a valve tree on a wellhead andcomprising at least one separator for removing solids to clean thefluid. The hub or processing unit may be configured to be connected to atop of the valve tree or an upper end of a vertical bore of the valvetree. The hub or processing unit may comprise at least one connector.The connector may comprise a flange for mating with a complementaryflange of a vertical bore portion of the valve tree. The connector maybe provided on a body to which the separator may be mounted andsupported, for structurally supporting the separator upon the valvetree, e.g. on a top of the valve tree and/or an upper end of a verticalbore of the valve tree. The connector and/or the body may comprise athroughbore arranged to align with a bore of the valve tree for fluidlyconnecting the valve tree with the separator when connected to the valvetree, e.g. when connected by the flanges.

Embodiments of the invention can be advantageous as will be apparentfrom throughout the description, claims, and drawings.

Any of the various aspects of the invention may include the furtherfeatures as described in relation to any other aspect, whereverdescribed herein. For instance, any of the aspects may further compriseany feature defined in any one or more of the dependent claims appendedhereto. Features described in one embodiment may be combined in otherembodiments. For example, a selected feature from a first embodimentthat is compatible with the arrangement in a second embodiment may beemployed, e.g. as an additional, alternative or optional feature, e.g.inserted or exchanged for a similar or like feature, in the secondembodiment to perform (in the second embodiment) in the same orcorresponding manner as it does in the first embodiment.

DESCRIPTION AND DRAWINGS

There will now be described, by way of example only, embodiments of theinvention with reference to the accompanying drawings, in which:

FIG. 1 is schematic representation of an assembly comprising apparatusfor processing fluid from a well according to an embodiment of theinvention;

FIG. 2 is a part-sectional representation of the apparatus of FIG. 1 inclose up, the apparatus including a valve tree provided with a separatorand a flow tube;

FIG. 3 is a part-sectional representation of the apparatus of FIG. 2along the line I-I;

FIG. 4 is a part-sectional representation showing details of theseparator for the apparatus of FIG. 2 where the separator includes adegasser according to one embodiment of the invention;

FIG. 5 is a part-sectional representation showing details of theseparator for the apparatus of FIG. 2 where the separator includes asand cleaner according to another embodiment;

FIG. 6 is a part-sectional representation showing details of theseparator for the apparatus of FIG. 2 where the separator has parallelde-sanders, according to yet another embodiment;

FIG. 7 is a schematic representation of an assembly comprising apparatusfor processing fluid from a well according to an embodiment of theinvention;

FIG. 8 is a top view representation of part of the apparatus of FIG. 7;

FIG. 9 is a schematic representation of apparatus for processing fluidfrom a well according to another embodiment of the invention;

FIG. 10 is a schematic representation of apparatus for processing fluidfrom a well in an intervention mode according to an embodiment of theinvention;

FIG. 11 is a schematic representation of apparatus for processing fluidfrom a well in an intervention mode according to another embodiment ofthe invention;

FIG. 12A is a schematic part-sectional representation of a valve treeprovided with a separator and a removable flow tube, wherein the flowtube is in a stand-by position, according to an embodiment of theinvention;

FIG. 12B is a schematic part-sectional representation of a valve treeprovided with a separator and a removable flow tube, wherein the flowtube of FIG. 12A is in an deployed position;

FIG. 13A is a schematic part-sectional representation of a valve treeprovided with a separator and a retractable flow tube, wherein the flowtube is in an inactive position, according to an embodiment of theinvention;

FIG. 13B is a schematic part-sectional representation of a valve treeprovided with a separator and a retractable flow tube, wherein the flowtube of FIG. 12A is in an active position;

FIG. 14 is a schematic part-sectional representation of apparatus forprocessing fluid from a well where a separator includes parallelde-sanders according to an embodiment of the invention;

FIG. 15 is a perspective part-sectional representation of apparatus forprocessing fluid from a well according to another embodiment; and

FIG. 16 is a perspective part-sectional representation of the apparatusof FIG. 15 using an inserted flow tube in the valve tree forfacilitating the supply of production fluid to the de-sander and passageof cleaned production fluid downstream away from the de-sander.

With reference first to FIG. 1, part of an offshore platform 1 isillustrated with apparatus 10 provided for processing fluid from a well.The apparatus 10 includes a valve tree 12 arranged at a valve tree deck2 of the platform. The valve tree 12 is connected to the top of awellhead 5 of the well.

The platform 1 also has a hatch deck 3 above the valve tree deck 2 asindicated in FIG. 1. The hatch deck 3 has hatches 4 a-4 c whichfacilitate access to valve trees positioned below, at the valve treedeck 2.

During production from the well, production fluid travels downstreamthrough the apparatus 10 to a well choke 30, and onward to a downstreamprocessing system 50.

The apparatus 10 includes a processing unit 16 in the form of a dynamicde-sander (a separator) which is mounted onto the valve tree 12. Thede-sander receives the production fluid from the well through a mainbore 13 of the valve tree 12, as indicated by arrows A, removes unwantedsolids such as sand or the like from the raw production fluid from thewell, and produces an output of clean production fluid from theprocessing unit 16 which no longer contains the removed solids.

The apparatus 10 includes a flow tube 17 which in FIG. 1 is insertedinside the valve tree 12 bridging a service wing bore 14 and aproduction wing bore 15 of the valve tree 12 (the flow tube 17constituting a “bridge tube”). The clean production fluid is fed fromthe de-sander, back through the valve tree 12 through the flow tube 17,as indicated by arrows B, and onward to the well choke 30 and to thedownstream processing system 50, which may be a downstream processingsystem as described hereinabove.

In this way, the well choke 30, the downstream processing system 50, andthe pipework between the valve tree 12 and the processing system 50 canavoid undesired exposure to the solids content in the raw fluid from thewell.

With further reference to FIGS. 2 and 3, the apparatus 10 can be seen infurther detail. The valve tree 12 is in the form of a typical Christmastree on a wellhead. The main bore 13 is vertical and has an upper boreportion for accessing a top end of the main bore 13. The tree 12additionally has side bores including the production wing bore 15 andthe service wing bore 14 for alternative entry or exit routes throughthe tree to the well.

The valve tree 12 includes two main bore valves 18, 19 which canselectively be closed to shut off the well providing a double barrieragainst well pressure, or opened to allow fluid flow through the valvetree 12. As can be seen, the main bore valves 18, 19 are positioned at alocation along the main bore below the level of the service wing andproduction wing bores 14, 15.

The service wing bore 14 has a service wing valve 24 for closing/openingthe service wing bore 14, and similarly the production wing bore 15 hasa production wing valve 25 for closing/opening the production wing bore15. When closed these valves 24, 25 seal the service wing and productionwing bores 14, 15 to prevent fluid flow therethrough. Conversely, whenthey are open, access to the valve tree 12 and fluid flow is permitted.The upper bore portion of the main bore 13 also has an upper main bore,provided with swab valve 23 for closing/opening the upper main boreportion 13 for preventing/permitting fluid communication and/or accesstherethrough.

As will be appreciated, the valves 18, 19, 23, 24 and 24 are merelyillustrated schematically in the figures. Each of these valves may be inthe form of a ball valve or the like, having a barrel which is activatedby operation of the valve and which obturates the bore to close it, andseals against a wall section of the bore to seal against well pressure.

In another example as illustrated in FIG. 4, the apparatus 10 has aprocessing unit 116 in place of the processing unit 16 described above.The processing unit 116 is illustrated in the form of a hub in which ade-sander 127 is mounted together with other components for processingfluid, providing a compact unit with the necessary components forprocessing and cleaning the fluid from the well.

In particular, the processing unit 116 in this variant includes adegasser 126 for removing gas from the production fluid, a de-sander 127for removing solids, and a solids container 128 for storing theseparated solids from the de-sander 127 for disposal. The processingunit 116 includes a pipe section 122 (constituting a body with athroughbore) provided with a connector 121 for rigidly connecting theprocessing unit to the top of the valve tree 12. The interior of thepipe section 122 is arranged to be in fluid communication with the mainbore 13 of the valve tree 12. The de-gasser 126, the de-sander 127, andthe solids container 128 each comprise a processing tank which ismounted to the pipe section 122 via connecting brackets 129 a, 129 b.The connector and pipe section 121 provide for mounting of the de-sander127 and the other components and for attaching these onto the top of thevalve tree 12, providing both fluid connection and structural supportfor the de-sander 127. The connection to the valve tree 12 is such thatthe valve tree 12 bears the weight of the processing unit 116. In otherexamples, the de-sander 127 and the other equipment may be mounted on arigid frame, e.g. of steel or other high-strength material, which isconnected onto the valve tree 12.

During production of fluid from the well in the present example, theproduction fluid travels upward through the main bore 13 of the tree 12and along the pipe section 122. The fluid enters the degasser 126through a port in the wall of the pipe section 122 and through adegasser inlet 126 i. Gas from the fluid is bled off through a gasoutlet 126 g, and the degassed fluid exits the de-gasser through outlet126 x and into the de-sander 127 i via a de-sander inlet 127 i. Thedashed line R indicates the route of the fluid from the degasser to thede-sander 127.

In the de-sander 127, solids are separated out of the fluid to produce aclean production fluid no longer containing the removed solids. Thecleaned production fluid then exits the de-sander 127 through the outlet127 x, and passes through a flow line and back through the valve tree 12via the flow tube 17, and onward to the choke 30 and the processingsystem 50 downstream. The gas from the outlet 126 g is reintroduced andcombined with the cleaned production fluid, e.g. via a connection (notshown) to the outlet 127 x.

The solids which are separated out by the de-sander 127 may selectivelybe disposed from the de-sander 127 through a first solids outlet 127 sor passed on to the solids container 128 through a second solids outlet127 t and into the tank of the solids container through inlet 128 i.Solids from the solids container 128 may later be disposed via an outlet128 x.

Valves on the inlet and/or outlet lines are indicated with solid fill toindicate a closed valve and no fill to indicate an open valve. Thevalves may all be controllable so as to be opened or closed to controland guide the flow of fluid, and optionally shut off fluid flow,according to requirements. In FIG. 4, the valves are closed on the firstand second outlets 127 s, 127 t. Thus, separated solids are not beingtransferred from the de-sander to the solids container 128, in theinstance shown. The flow valves on the inlets 126 i, 127 i and theoutlet 127 x are open, allowing for the production fluid to progressthrough the degasser and then the de-sander before the cleanedproduction fluid travels through the valve tree 12 downstream.

The de-sander 127 may be one as described in WO03099448 (Arefjord).

Turning now to FIG. 5, another example is illustrated with a differentprocessing unit 216 in the apparatus 10 in place of those describedabove. Features corresponding to ones described in relation to theprocessing unit 116 are denoted with the same reference numerals butincremented by one hundred, and may not be explicitly described againhere.

In this case, the processing unit 216 does not have the degasser, butinstead has a solids cleaner 220 mounted on a pipe section 222 viaconnecting brackets 229 a, 229 b, together with a de-sander 227 and asolids container 228.

Production fluid from the well travels upward from the main bore 13 ofthe valve tree 12, along the pipe section 222 and through a port in thewall of the pipe section 222 into the de-sander 227 via the de-sanderinlet 227 i. The path taken by the fluid entering the de-sander 227 isindicated by the broken line R in FIG. 5. Cleaned production fluid fromthe de-sander 227 is then circulated back to the valve tree 12 from theoutlet 227 x in the same manner as described above.

Separated solids contained in the solids container 228 x may betransferred via the solids outlet 228 x to the solids cleaner 220,entering the solids cleaner 220 through the cleaner inlet 220 i. In thesolids cleaner 220, the solids may be contained in a tank in which thesolids undergo treatment to remove contaminants from the solids. Thedecontaminated or cleaned solids may then be disposed from the solidscleaner 220 via an outlet 220 x.

In FIG. 6, another example is illustrated with a different processingunit 316 in the apparatus 10 in place of those described above. Featurescorresponding to ones described in relation to the processing units 116or 216 are denoted with the same reference numerals but incremented bytwo hundred or one hundred respectively, and may not be explicitlydescribed again here.

In this variant, the processing unit 316 has two parallel de-sanders 327a, 327 b provided with corresponding solids containers 328 a, 328 b, allwhich are mounted hub-wise together on a pipe section 322 connected viathe connector 321 to the valve tree 12. The de-sanders 327 a, 327 b areprovided on either side of the pipe section 322. The pipe section 322 isin fluid communication with main bore 13 of the valve tree 12.

In the example of FIG. 6, during production, production fluid passesupward from the valve tree 12 along the pipe section 322 and enters intothe de-sanders 327 a and 327 b through respective flow ports through thewall of the pipe section 322 and respective de-sander inlets 327 i.

Full diameter access to the main bore 13 of the valve tree 12 isprovided by the pipe section 322, which can be beneficial for performingwell intervention or other operations in the well whilst the processingunit is installed. This functionality will be described in furtherdetail below.

Referring now to FIG. 7, apparatus 110 for processing fluid from a wellis installed on the offshore platform 1. The apparatus 110 includes thevalve tree arranged as in the embodiments above with a flow tube 17arranged inside the tree. In this example, however, a processing unit400 is provided in contrast to those of the apparatus 10 describedabove.

The processing unit 400 is a compact unit with components mounted in ahub, designed to be deployed and installed in the location A, bylowering the processing unit 400 through the opening of the hatch 4 bonto the valve tree 12. The width of the processing unit 400 istherefore less than the lateral extent of the hatch 4 b to allow it tofit through the opening. The processing unit 400 occupies only the spacebelow the hatch, within the lateral dimension of the opening of thehatch 4 b in the hatch deck 3. The part of the pipe section 422 betweenthe processing unit 400 and the top of the valve tree 12 in this exampleis made sufficiently short to fit the de-sander within the space betweenthe valve tree deck 2 and the hatch deck 3.

In the installation location A as shown, the processing unit 400 isattached to the valve tree 12 via a connector hub 421 and a pipe section422 which provides for fluid communication and/or access to the mainbore 13 of the valve tree from a top end of the processing unit 400, ifrequired. The processing unit 400 is disposed in a column of space Cextending upward from the valve tree through the opening of the hatch,the column width being defined by the width of the hatch opening.

The processing unit 400 includes first and second de-sanders 427 a, 427b, a choke manifold 461, and an emergency shutdown (ESD) valve 462.Production fluid passes via the pipe section 422 into the de-sanders 427a, 427 b, through a choke of the choke manifold 461 and through the ESDvalve 462. In some variants, the choke manifold 461 may provide a wellchoke which may be controllable to control fluid flow and/or shut offflow from the well. In this variant, the choke in the choke manifold 461may replace the well choke 30, so that clean fluid from the de-sander427 a, 427 b may travel directly the downstream processing system 50without going via the normal well choke 30, or without needing to usethe well choke 30.

Fluid circulates otherwise as described in the embodiments above. Thatis, the production fluid travels upward through the main bore 13 of thevalve tree 12, and passes through the de-sanders 127 a, 127 b. Cleanproduction fluid from the de-sanders 127 a, 127 b travels back out ofthe processing unit 400 through the valve tree via the flow tube 17 andonward downstream from the valve tree 12, e.g. to the downstreamprocessing system 50.

FIG. 8 illustrates the arrangement of the processing unit 400 from abovewith the hatch 4 b open and when installed in the installation locationA and/or when being lowered through the opening of the hatch 4 b. As canbe seen, the processing unit 400 fits through and is arranged laterallywithin the opening of the hatch 4 b. The tanks of the de-sanders 427 a,427 b are eccentrically positioned to either side of the pipe section422. The pipe section 422 is provided centrally, and provides an accessconduit for communication with the main bore 13 of the valve tree 12when the processing unit 400 is mounted upon the tree 12. The tanks ofthe de-sanders 427 a, 427 b are rigidly connected to the pipe section422 via connecting members 429 a, 429 b, and to the connector hub 421(not shown in FIG. 8), permitting the lowering of the de-sander as aunit from above the hatch deck, through the hatch 4 b and into positionA on the valve tree. The processing unit 400 may be fitted with a pipeflange, e.g. on the connector hub 421, for sealed mating with andconnection to a corresponding flange of tree above the swab valve 23.

In FIG. 9, a variant is exemplified where the processing unit 400 isinstalled above the hatch deck 3, in an installation location B. In thiscase, the pipe section 422 includes a riser 422 r which passes upwardthrough the opening of the hatch 4 b between the processing unit 400 andthe valve tree 12. The processing unit 400 is confined to the column ofspace C through the opening of the hatch, which can advantageouslyprovide for the processing unit 400 to be used on the rig withoutintruding into other areas of the hatch deck. The processing unit 400may also remain installed while full diameter access to the well may beprovided via the pipe section 422 and the riser 422 r. Production fluidfrom the well thus passes up from the well through the valve tree 12through the riser 422 r and into the de-sanders 427 a, 427 b beforereturning from the processing unit 400 back through the valve tree 12and the flow tube 17 as in the embodiment of FIG. 8.

Turning to FIG. 10, the apparatus 110 is illustrated in another mode ofoperation for performing a well intervention in the well. The processingunit 400 is installed in the location A, on the top of the valve tree12, and is used to clean fluid returning from the well. An interventiontool 40 is being lowered into the well through the pipe section 422. Theflow tube 17 as utilised in the above described embodiments is removedand not used in this mode. There is therefore no flow tube 17 in themain bore 13 of the valve tree, and the intervention tool 40 has fulldiameter bore access to the well through the pipe section 422 and thevalve tree 12. In this case, the pipe section 422 includes anintervention riser 422 i which extends through the hatch 4 b up from thetop of the processing unit 400 and connects with an interventioninterface above the hatch 4 b. The intervention interface may includeintervention control equipment, such as valves for pressure containment,etc., during an intervention operation.

The intervention tool 40 is deployed on a wireline 41 in this example.However, it will be appreciated that the intervention tool 40 may be ofmany different kinds, depending upon the nature of the interventionoperation to be performed in the well. Accordingly, the interventiontool in other embodiments may be deployed on jointed pipe, or coiledtubing, instead of the wireline 41.

Likewise, in certain embodiments, operation of the intervention tool mayrequire circulation of a fluid into the well, e.g. through the centre ofa jointed pipe string, and back out of the well through an annulus up tothe surface. In such an embodiment, the processing unit 400 can be usedto process the returning fluid from the annulus, e.g. to remove solidsfrom the fluid. Clean fluid, without the removed solids, may then bepassed via the well choke, which may be operated for pressure control orthe like of the well during the intervention.

The arrangement of the processing unit 400 illustrated in FIG. 10 maytherefore be utilised with production wells during production of oil andgas from the well, but also during well construction, or when productionof oil and gas is not taking place.

In FIG. 10, the route of the fluid from the wellhead 5 upward into thepipe section 422 and out of the processing unit 400 is indicated by abroken line R. The clean fluid from the processing unit 400 isintroduced into a flow line downstream of the production wing 15 of thetree. Preferably, a connecting line 463 from the processing unit 400 isconnected to a pipe 31 between the production wing and well choke 30. Ifthere is a connection valve already provided in the pipe 31, then thiscan conveniently be utilised for connecting the line 463 with the pipe31. In this case, the main bore 13 of the valve tree 12 is unavailableas it is occupied by the intervention tool 40, such that the point ofconnection for the clean fluid to the pipe 31 is made without using theflow tube, but still preferably close to the valve tree 12.

FIG. 11 shows the offshore platform 1 where the apparatus 110 isarranged with the processing unit 400 above the hatch 4 b in theinstallation location B. The processing unit is installed as in FIG. 9,but in this case is in an intervention mode with an intervention tool 40being lowered into the well through the pipe section 422. The processingunit 400 is connected and operates as described in relation to FIG. 10.In FIG. 11 however, the pipe section 422, through which access for theintervention tool 40 is provided for accessing the well via the mainbore 13 of the valve tree 12, includes both an intervention riser 422 iabove extending from the processing unit to connect with theintervention interface above and a valve tree riser 422 r extending fromthe valve tree 12 through the opening of the hatch 4 b to the connectorhub 421 of the processing unit 400.

In general, it can be appreciated that the flow tube as described abovemay be configured in different ways in other embodiments of theinvention, but still being capable of its basic performance in allowingthe flow of clean fluid to traverse the main bore 13 of the tree 12between the service wing inlet and production wing inlet. In the figuresabove, see for instance FIG. 5, a fixed variant of the flow tube 17 isillustrated, where the flow tube 17 is fixed to a flange 67 which isattached to a mating flange on the service wing of the tree. Whenattached and in place for use, the flow tube 17 extends from the flange67 across the main bore 13, as illustrated in FIG. 5. When the flow tubeis to be removed, e.g. when full access to the main bore 13 is needed,the flange is disconnected and removed so as to extract the flow tubefrom the tree 12.

Turning to FIGS. 12A and 12B, a different flow tube 517 is employedinstead of the fixed flow tube 17 as described above. More specifically,in FIG. 12A, an embodiment of apparatus 510 for processing fluid from awell is depicted, including a processing unit 516 including a de-sandermounted on the valve tree 12. It shows in particular a variant using aremovable flow tube 517. In a mode where access to the main bore isrequired by other equipment, and the flow tube 17 needs to be removedfrom the main bore, e.g. in the intervention modes of FIG. 9 or 10, theflow tube 517 can be stored in the valve tree, e.g. inside the servicewing 14 as illustrated in FIG. 12A. In order to store the flow tube 517,a housing 565 is connected to the service wing for containing the flowtube 517 inside the valve tree 12 in a stowed position, with the servicewing valve 24 closed between the housing 565 and the main bore 13. Thehousing 565 typically remains fixed in place to the service wing whilethe flow tube is in use. When the flow tube 517 is to be deployed in itsuse position where it straddles the main bore 13, a suitable deploymenttool may be used to position it. When it is to be retrieved, a retrievaltool may be used in order to retrieve (e.g. “fish”) the flow tube backinto the housing 565 where the tube 517 is kept until further needed.The deployment and retrieval tools may therefore need to be deployedwhen the flow tube is to be deployed or retrieved, and may be removedfrom the area of the valve tree 12 at other times. Permanent deploymentor retrieval tools are not required, which may have benefits in terms ofspace. As the flow tube 517 can be housed within the housing on theoutside of the service wing valve 24, the service wing valve 24 can beutilised to seal the main bore 13. With the flow tube removed from themain bore and contained within the housing 565, there would not be flowthrough the service wing valve, and a flow valve 564 in the line whichcould otherwise send the clean fluid from the processing unit 516through the tree would be closed as indicated.

FIG. 12B illustrates the apparatus 510, with the flow tube 517 deployedand inserted to bridge the main bore 13 for circulation of clean fluidfrom the processing unit 516 into the tree 12 through the flow tube 517and onward downstream, the valve 564 now open.

In FIGS. 13A and 13B another variant is illustrated with a retractableflow tube 717 employed to provide for directing the flow through thetree 12. In this case, the flow tube 717 is connected to an actuator 765which is connected onto to the service wing 14. The actuator 765 has anactuation mechanism 766 which is operable to move the flow tube 717 froma retracted position (inside the valve tree 12) as illustrated in FIG.13A into an extended, operational position as illustrated in FIG. 13B,and vice versa. In the operational position, the flow tube 717 reachesacross the main bore 13 and can direct cleaned fluid from the de-sander716 through the flow tube 717 and the valve tree 12 as indicated in FIG.13B, and onward downstream to the production system. In this variant,the actuator 765 and actuation mechanism 766 typically remains in placeand on standby on the valve tree and can simply be activated to actuatethe flow tube 717 to put it in the required position, either retractedor extended, when needed.

In the above, the valve tree is described as being provided on aplatform or rig. However, it should be appreciated that valve treesconfigured in the same manner, having a main bore accessible from thetop, a service wing and a production wing, may also be found on land orsubsea. The de-sander, etc., may therefore be connected and used on aland or subsea valve trees in the same way as described above for theplatform or rig tree.

While the above examples illustrate a processing unit that receivesfluid from one well, it will be appreciated that several wells may be inoperation simultaneously, where the valve trees associated with therespective wells are collected together at a manifold (e.g. subseamanifold) or on a valve tree deck of a platform. The processing unit mayin such cases be located at or on the valve tree of one well, but alsoused to receive fluid from another well, e.g. a neighbouring or anadjacent well, by routing the flow from the other well throughappropriate flow lines to the processing unit. The processing unit mayin such cases be used both to clean the fluid of the well on which theprocessing unit is provided and the fluid of the neighbouring well, e.g.by combining the fluid from the two wells and leading the combined fluidinto the de-sander for removal of solids. The cleaned fluid producedfrom the processing unit may travel downstream through the valve tree onwhich the processing unit is provided and/or through the valve tree ofanother well (e.g. the neighbouring or adjacent well), e.g. via aninserted flow tube in the relevant valve tree or trees and byappropriate flow lines between the valve trees.

Furthermore, example embodiments are described above where the valvetree supports and bears the weight of the processing unit and de-sanderby way of the processing unit being connected to the top of the valvetree. It will be appreciated that in other embodiments, the valve treemay not bear the weight of the processing unit and de-sander, or mayonly do so partially, for instance by providing some additionalsupporting means for supporting the processing unit which relieves thevalve tree of the full load of the processing unit. If for example thereis a deck above the valve tree, the processing unit can be held on asupport on the deck so that the weight of the processing unit orde-sander is not transferred to the valve tree. This may be useful ifthe weight-bearing capacity of the tree is limited and might be exceededif transferring the entire weight of the processing unit to the valvetree.

FIG. 14 illustrates a solution using a stinger 622 for guiding the flowof fluid from the well into the de-sander and for guiding the cleanedflow from the de-sander through the tree 612 and downstream to thedownstream processing system. This solution may also be applied onsubsea, land, or rig or platform based valve trees. It can beparticularly useful in valve trees where there is no service wing, sinceit avoids access through a service wing. The solution of FIG. 14 byusing a stinger provides an alternative means for installing thede-sander, instead of using the bridging flow tube which crosses themain bore as described in the examples above.

More specifically, in the example of FIG. 14, apparatus 610 includes aprocessing unit 616 which is mounted upon a valve tree 612. Theprocessing unit 616 has a stinger 622 through which the processing unit616 fluidly and physically connects with the valve tree 612. The stinger662 has an outer tube 662 t and an inner tube 662 i. The stinger 662penetrates into the main bore 613 of the valve tree 612 and sealsbetween the outside of the stinger 662 and an inner surface of the mainbore 613 by way of two sets of seals 667, 668. The penetrating end ofthe stinger 662 s is tubular and an inner tube 622 i is inserted alongthe vertical main bore 613. This allows fluid from the well to flowupward inside the inner tube 662 i of the stinger 662 s and into thede-sanders 627 a, 627 b of the processing unit 616. The path of the flowto the de-sanders 627 a, 627 b is indicated by the broken line witharrows W. An important feature of this example is that it provides forinstallation of the processing unit on the valve tree and establishesthe necessary flow paths without needing access through a service winginlet of the valve tree.

Clean fluid from the de-sanders 627 a, 627 b is directed into a sealedannulus in the valve tree 612 between an outside of the lower part 622 sof the stinger 622 s and a wall of the main bore 613 of the valve tree612. The clean fluid may also travel via an annular space between theouter and inner tubes 662 i, 662 t of the stinger 662. The path of theclean fluid is indicated by the broken line and arrows V. The cleanfluid then passes out of the valve tree through the production wing bore615 and associated valve 625. The service wing is not engaged in thisset up, so this arrangement, utilising the stinger, can be applied wherethere is no service wing inlet available such as may be found on asubsea tree, or if a service wing of the tree is otherwise occupied.

The solution of FIG. 14 may be convenient since the stinger can belowered directly onto the top of a main bore of the valve tree so thatboth the de-sander is installed and the necessary flow path for fluid isset up for directing fluid into the de-sander and cleaned fluid backthrough the valve tree. Since it does not require access to the servicewing, it provides a solution for valve trees where there is no servicewing for installing a flow tube across the vertical main bore betweenthe service wing inlet and the production wing outlet, or if for someother reason the service wing may not be accessible. Subsea valve treesin many cases do not have a service wing inlet, often having only ahorizontal production bore (“production wing”) for production fluid, andan access inlet aligned with a main bore in the tree through whichequipment can access the wellbore where needed. Therefore, the solutionof FIG. 14 may be particularly applicable and the only alternative forsome subsea valve trees. In other cases such as on a rig or a platform,there may be several valve trees on the valve tree deck in relativeclose proximity to one another and little space for access adjacent tothe tree. The FIG. 14 solution may thus be useful in valve trees onplatforms or rigs, even if the valve tree has a service wing. It can ofcourse also be applied similarly to a land or a subsea valve tree, evenif the valve tree has a service wing, where there may also be lack ofaccess or other reasons to prefer the stinger arrangement to insertionof a horizontal flow tube via the service wing inlet.

In general, the stinger configuration can be advantageous in that theprocessing unit 616 can be provided and installed on the wellheaddirectly and ready for use, simply by guiding the stinger into the mainbore of the tree until it abuts and sits in the correct position withthe seals 667, 668 engaged. This can be beneficial in the case of subseawells, where the wellhead is at the seabed with a subsea valve tree onthe wellhead.

When in use as seen in FIG. 14, the stinger 662 occupies space in themain bore of the tree reducing accessibility to the well. If fulldiameter access is required, e.g. for performing an intervention, theinner tube 662 i of the stinger can be removed from the outer tube 662t, e.g. by fishing it out on a wireline or the like. Thus, interventionscan be performed by lowering intervention tools through the outer tube662 t while the processing unit 616 remains in place on the valve tree.It will be appreciated outer tube 662 t in this embodiment in effectprovides a pipe section to which the de-sanders in this variant arefixed and mounted in place.

FIG. 15 exemplifies in more detail how a processing unit 816 or hub maybe configured and supported on the valve tree 812 in practice. Thismanner of connecting the processing unit 816 may be adopted in any ofthe embodiments described above. The processing unit 816 includescomponents as described in relation to FIG. 6. The processing unit 816has two de-sanders 827 a, 827 b (separators) and respective solidscollectors 828 a, 828 b. The de-sanders 827 a, 827 b can operate inparallel to remove solids from the hydrocarbon production fluid from aproducing oil and gas reservoir during hydrocarbon production. The pipesection 822 is connected to a top of the valve tree 812, on an upper endof a vertical bore of the tree 812. A connector 821 at a lower end ofthe pipe section mates to a flange at the top of the valve tree 812 tosecurely and sealingly connect the end of the pipe section 821 onto thetop of the valve tree. The weight of the processing unit is transmittedthrough the pipe section to the valve tree 812.

In other embodiments, a vertical riser is connected to the top of thevalve tree 812 and the pipe section 822 is connected to an upper end ofthe riser. Alternatively, the pipe section 822 may be a riser having alength so that when connected to a tree, the tanks of the processingunit are spaced vertically apart from the top of the valve tree by adesired distance, e.g. greater than that indicated by FIG. 15.

As can be seen, each de-sander 827 a, 827 b comprises a tank 880 a, 880b and each solids collector 828 a, 828 b comprises a tank 890 a, 890 bfor collecting and containing the removed solids. The tanks are pairedup so that the tanks 880 a, 890 a associated with the separation of thede-sander 827 a are positioned in different locations, one above theother, along the pipe section 822. The tanks 880 b, 890 b associatedwith the de-sander 827 b are similarly arranged in respective positionsalong the pipe section 822, one above the other, on the other side ofthe pipe section 822. Furthermore, the tanks 880 a, 880 b, 890 a, 890 bare arranged as upright cylinders. In other variants, the cylinders maybe made longer vertically to increase their capacity without impactingon the radial footprint, or in yet further variants additional tankse.g. de-sander and/or solids collector tanks, may be added along thepipe section, without increasing the radial footprint. Further tanks mayalso be placed in other locations around the circumference of the pipesection 822 without expanding a maximum diameter.

As seen in FIG. 15 production fluid from the wellhead, indicated byarrows R, travels through the valve tree 812, through the pipe section822, and is then received by the de-sanders 827 a, 827 b.

The cleaned production fluid from the de-sanders 827 a, 827 b indicatedby arrows P, travels downstream from the de-sander through productionflow lines for onward processing and refining, free from sand or otherrock fragments from the subsurface formations. The provision of theprocessing unit 816 on the valve tree 812 can thus relieve thedownstream flow line components from abrasion and wear as typically canbe a problem in late field development scenarios. Production rates maytherefore be increased as a result.

Although not explicitly illustrated in FIG. 15, it can be appreciatedthat the cleaned production fluid P may follow a flow path through thetree, e.g. provided by inserting a tube into the bore of the tree, suchas a bridge tube which crosses the vertical main bore from the serviceto the production wing or a stinger tube inserted into and parallel withthe main bore. Alternatively, the cleaned production may pass through atube which is simply connected to the production line at a convenientlocation close to the valve tree, e.g. where there is an existing accesspoint.

FIG. 15 illustrates components of the de-sander 827 a in the interior ofthe tank 880 a. The de-sanders (constituting separators) of any of theembodiments described above may be configured similarly.

The de-sander 827 a (a separator) is configured to produce a fluidcyclone inside the tank 827 a, so that when the production fluid entersthe tank, the de-sander sets the production fluid in motion in acyclonic flow. This may be done in various. In the example of FIG. 15,has a rotatable body, e.g. a fin or impeller, inside the tank 880 awhich engages the production fluid and rotates to impart a rotationalforce on the production fluid. The production fluid enters the tank 880a at an upper end. The rotational force urges the fluid radially outwardtoward the wall of the tank, while at the same time being subject togravity, providing a cyclonic or rotational flow as indicated by arrowsC. The interior of the tank 880 is in the form of a cylindrical chamber.This separation of the solids in the production fluid have a differentmass or density to liquid or gas components, and by virtue of this factthey are affected to different degrees by the rotational andgravitational force components, so that they separate out. The solids,i.e. rock fragments or particles of minerals, sand, etc produced fromthe reservoir formation, drop out of the flow and fall to the bottom ofthe tank 880 a and collect in the tank 890 b of the solids collector 828a. The liquid component or fluid combination of liquid and gas may passonward downstream through an outlet in the wall near an upper end of thetank 880 a, and constitutes cleaned production fluid which then travelsaway downstream as indicated by arrows P.

The rotatable body, e.g. fin or impeller (not shown) is disposed insidea cylindrical screen 882 in the tank. The body is mounted to a verticalshaft 884 inside the tank 880. The shaft is connected to a motor 886which operates to turn the shaft 884 about its long axis. By operationof the motor 886 therefore the rotatable body is rotated about avertical axis inside the screen 882, at a speed which provides thenecessary impetus to the production fluid being received in the tank toknock out the solids. The production fluid is driven outward toward thewall of the screen, through openings in the screen, and into the regionbetween an outside of the screen and the wall of the tank, where theproduction fluid flows as indicated by arrows C, and the solids fall tothe bottom of the tank.

The above represents a dynamic de-sander technique where the cyclonicflow is actively enhanced by operating the rotational device using themotor. The de-sander described in WO03099448 (Arefjord) is anotherexample of a cyclonic, dynamic de-sander. It may be appreciated thatcyclonic flow may be obtained in other ways, e.g. by jetting theproduction fluid to drive the production fluid from a tangential inletaround a curved inner wall of a cylindrical chamber at sufficient andappropriate velocity. This may provide a cyclonic flow without use ofthe actively rotated rotational body driven by the motor.

FIG. 16 is an implementation of the same arrangement as FIG. 15 with aspecific flow path solution for directing the cleaned production fluid Paway from the de-sanders 827 a, 827 b through an inside of the valvetree 812. In this case, a flow tube 862 is inserted into the verticalmain bore of the valve tree 812. The flow path is similar to thatcreated in FIG. 14. An upper end of the flow tube is positioned insidethe pipe section 822 and the lower end of the flow tube 862 ispositioned inside the main bore of valve tree 812 below the productionwing and service wing bores. The unprocessed production fluid R passesinto the lower end of the flow tube, through the flow tube 862, andexits the flow tube 862 at the upper end. The production fluid R is thenreceived in the de-sanders 827 a, 827 b which operate as describedabove. The cleaned production fluid P returns on a flow path between anoutside of the flow tube 862 and a wall of the interior of the valvetree 812.

In each of the examples of FIGS. 4 to 11 and 14 to 16, full diameteraccess can be provided to the valve tree. In some of these examples, itis necessary to remove the flow tube used for providing the flow pathfor the cleaned production fluid, in order to obtain the full diameteraccess. The flow tube (see the stinger in FIG. 14) may be removed on atemporary basis while the processing unit remains installed, so that anintervention operation or other operation which may be reliant upon theability to have full diameter access can be performed. With reference tothe example of FIGS. 15 and 16 therefore, the arrangement in FIG. 15illustrates a configuration of full bore access whereas in FIG. 16 thereis not full diameter access due to the presence of the flow tube 862.

By providing full diameter access, an intervention string can be placedin the passageway (in this example inside the pipe section 862) and belowered from a location above the valve tree 812, into and through thevertical bore of the valve tree, unhindered by any restrictions in thepassageway or in main bore of the valve tree. Therefore, theintervention string may have a diameter which is equal to the innerdiameter of the main bore of the valve tree (subject to tolerances offit), and yet be allowed to pass into and through the valve tree 812.The passageway in the pipe section 862 may therefore have an internaldiameter which is greater or equal to that of the valve tree over theentire part of its length which will be exposed to the maximum diameterof the intervention string. The same functionality can be provided inthe embodiments of FIGS. 4 to 11 and 14 to 16. Such a configuration istypically termed full bore access, and can be an important feature toavoid having to remove processing equipment to perform wellintervention, and let the processing unit 816 stay in place. This mayallow an intervention to be performed efficiently and production to beresumed quickly. In FIG. 16, access to the wellbore may advantageouslybe obtained albeit not full bore, through the flow tube while the flowtube 862 remains inserted. The interior passageway of the flow tube 862is of a smaller diameter than the valve tree and in effect is arestriction, but this may not critical in specific applications.

In any of the examples herein, the production fluid may comprisehydrocarbons e.g. oil and gas from an oil and gas reservoir in thesubsurface, and the solids which are removed by the separator maycomprise grains or particles of rock or sand as may typically enter thewellbore in the far reaches of the wellbore together with thehydrocarbons from the reservoir. In all examples also, the valve treemay be connected to the top of the wellhead so as to be supported uponthe wellhead.

The embodiments described above may be advantageous in various ways. Inparticular, they can allow the ability to clean well fluids very closeto the valve tree, before entering downstream choke or processingequipment which may be sensitive to solids exposure or the like. Theapparatus can be provided space effectively and installed efficiently asa pre-provided compact unit, and may remain installed and used to cleanfluid during interventions in a well where full bore access may beneeded.

Various modifications and improvements may be made without departingfrom the invention herein described.

1. An assembly for an oil and gas production platform or rig, theplatform or rig having a Christmas tree deck and a hatch deck above theChristmas tree deck, the assembly comprising: a Christmas tree connectedto a top of a wellhead on the platform or rig, the Christmas treelocated at the Christmas tree deck; and a processing unit comprising atleast one separator, positioned above and connected onto a top of theChristmas tree, the Christmas tree bearing at least partially the weightof said separator; wherein the separator is operable for receivingproduction fluid from at least one oil and gas production well andremoving solids to clean the production fluid.
 2. An assemblycomprising: a Christmas tree connected to a top of a wellhead, theChristmas tree having a vertical bore for accessing the well by anintervention or another tool lowered on a wireline or tubing from abovethe vertical bore through said tree; and a processing unit comprising atleast one separator, positioned above and connected onto a top of theChristmas tree, the Christmas tree bearing at least partially the weightof said separator; wherein the processing unit is further arranged toprovide full diameter access to the vertical bore of the Christmas tree;and wherein the separator is operable for receiving oil and gasproduction fluid from at least one well and removing solids to clean theproduction fluid.
 3. The assembly as claimed in claim 2 on an oil andgas production platform or rig, said platform or rig having a Christmastree deck and a hatch deck above the Christmas tree deck, wherein theChristmas tree is arranged at the Christmas tree deck.
 4. The assemblyas claimed in claim 1, wherein the separator comprises a de-sander. 5.The assembly as claimed in claim 1, wherein the separator comprises ade-sander having a processing tank mounted in the processing unit. 6.The assembly as claimed in claim 5, wherein the de-sander has anassociated solids container comprising a processing tank for containingremoved solids transferred from the de-sander in order to be laterdisposed of.
 7. The assembly as claimed in claim 1, wherein theprocessing unit comprises first and second de-sanders operable inparallel to clean the production fluid.
 8. The assembly as claimed inclaim 1, wherein the processing unit includes a degasser comprising aprocessing tank, for removing gas from the production fluid upstreamfrom a de-sander.
 9. The assembly as claimed in claim 1, wherein theprocessing unit has a vertical conduit or passageway aligned with thevertical bore of Christmas tree for deploying an intervention or othertool on a wireline or tubing into the valve tree.
 10. The assembly asclaimed in claim 9, wherein the processing unit comprises a verticalconduit aligned with a vertical bore of the Christmas tree, and theseparator is a de-sander, wherein the de-sander and a solids containerassociated with the de-sander are spaced apart in the processing unitalong the conduit or passageway.
 11. The assembly as claimed in claim 9,wherein the processing unit comprises a vertical conduit or passagewayaligned with a vertical bore of the Christmas tree, and the separatorcomprises a processing tank which extends longitudinally along thevertical conduit or passageway.
 12. The assembly as claimed in claim 9,wherein the conduit or passageway comprises a vertical pipe section. 13.The assembly as claimed in claim 9, wherein the processing unitcomprises a connector for connecting the processing unit onto the top ofthe Christmas tree.
 14. The assembly as claimed in claim 13, wherein theconnector is configured to mate with a top flange of an upper boreportion of the vertical bore of the Christmas tree.
 15. The assembly asclaimed in claim 9, wherein the processing unit comprises a mount formounting the separator therein.
 16. The assembly as claimed in claim 9,wherein the processing unit further comprises either or both of anemergency shut down valve and a choke.
 17. A method of equipping aChristmas tree for processing fluid from at least one oil and gasproduction well using an assembly for an oil and gas production platformor rig, the platform or rig having a Christmas tree deck and a hatchdeck above the Christmas tree deck, the assembly comprising: a Christmastree connected to a top of a wellhead on the platform or rig, theChristmas tree located at the Christmas tree deck; and a processing unitcomprising at least one separator, positioned above and connected onto atop of the Christmas tree, the Christmas tree bearing at least partiallythe weight of said separator; wherein the separator is operable forreceiving production fluid from at least one oil and gas production welland removing solids to clean the production fluid, wherein theprocessing unit has a vertical conduit or passageway aligned with thevertical bore of Christmas tree for deploying an intervention or othertool on a wireline or tubing into the valve tree; the method comprising:applying the processing unit to the Christmas tree such that theseparator is at least partially supported on top of the Christmas treewhereby said Christmas tree bears at least part of the weight of theseparator.
 18. The method as claimed in claim 17, which is performed toequip the Christmas tree on an oil and gas production platform or rig,said platform or rig having a Christmas tree deck and a hatch deck abovethe Christmas tree deck, wherein the Christmas tree is arranged at theChristmas tree deck, the method including the step of lowering theapparatus through a hatch in the hatch deck onto the Christmas tree, soas to locate the separator in place, at least partially supported on thetop of the Christmas tree.
 19. A method of performing an interventionoperation through the vertical bore of the Christmas tree of an assemblyfor an oil and gas production platform or rig, the platform or righaving a Christmas tree deck and a hatch deck above the Christmas treedeck, the assembly comprising: a Christmas tree connected to a top of awellhead on the platform or rig, the Christmas tree located at theChristmas tree deck; and a processing unit comprising at least oneseparator, positioned above and connected onto a top of the Christmastree, the Christmas tree bearing at least partially the weight of saidseparator; wherein the separator is operable for receiving productionfluid from at least one oil and gas production well and removing solidsto clean the production fluid; the method comprising: loweringintervention equipment through the vertical bore, while the separatorremains in place and is at least partially supported on the top of theChristmas tree.